Heat exchanger fin fastener



m N E w M A m RF @R m MA w GX E T A E H Set, 18. 1956 Filed March 4,1955 NIH ATTORNEY HEAT EXCHANGER FIN FASTENER George M. Certain,Tulsayokla.

Application March 4,1955, Serial No. 492,279

6 Claims. (Cl. 257-262.2)

This invention relates to finned tubing for heat exchangers and consistsmore particularly in new and useful improvements in a method and devicefor securing helical fin strips to lengths of tubing for use in heatexchanger units.

Inthefieldof heat exchangers, there are many forms of finned tubing inwhich a length of tubing ishelically wound with a strip of heatradiating material. In the fabrication of some of these heat exchangeelements, it is customary to form the fin by winding a continuousstraight strip or ribbon of metal into a Hat 'helical coil which issubsequently secured around its inner edge to the surface of the tube,by soldering. In others, the tube is fed and rotated in such a mannerthat a strip of thin metal will be wound around the tube and securedthereon, all in one operation. In this form the fin strip is usuallyformed in such a manner as to provide a securing edge by means of whichit can be secured to the tube by solder or the like.

In the past, most of the finned tubing of this type has been formed withcopper fins with which the operation of soldering has presented no greatdifficulty. However, more recently methods have been developed forhelically winding aluminum strips on brass tubes and as aluminum is moredifficult to solder than other metals previously used, means have beendevised to swedge the inner edges of the helical strips on to the brasstubes and although this system has been satisfactory in binding themajor area of the helical fin to the brass tube, it is still necessaryto solder or otherwise secure the extremities of the helical fin to thetube sections before the finned tubing is installed in a heat exchangerunit. Otherwise, it has been found that the extremities of the helicalfin have a tendency to dislodge which tends to weaken the entirestructure under the influence of vibration.

Even this minimum soldering operation has caused considerable difficultywhen aluminum strip is used for forming the helical fin, because of thefact that special aluminum solder is required and experience has shownthat this deteriorates very rapidly under service conditions.

It is therefore, the principal object of the present invention toovercome this difficulty by providing a specially designed fin fasteningdevice which may be formed of copper wire or other suitable metal wireadapted to be soldered to the supporting tube with conventional tinleadsolder and mechanically connected to the convolutions of the helical finat the extremities thereof, to firmly secure the fin in place on thetube.

A further object of the invention is to provide an auxiliary fasteningdevice for the extremities of helical fins which have been swedged on toa supporting tube, said fastening device being secured to the tube withordinary tin'lead solder and an organic flux which when applied willlast for the life of the tube.

With the above and other objects in view which will appear as thedescription proceeds, the invention consists ited States Patent M2,763,470 Patented Sept. 18, 1956 in the novel features herein setforth, illustrated in the accompanying drawings and more particularlypointed out in the appended claims.

Referring to the drawings in which numerals of like character designatesimilar parts throughout the several views,

Figure 1 is a side elevational view of a heat exchanger tube, brokenaway, showing the fin fastening devices applied to opposite extremitiesof the tube.

Figure 2 is an end elevational of the same.

Figure 3 is a top plan view of one end of a heat exchanger tube, showingone form of fin fastener, and

Figure 4 is a similar view of another tformof fastener which inpractice, is the preferred form.

In the drawings, referring first to Figure 1, a section of heatexchanger tubing is generally represented by the numeral 6 and consistsof a core 7 formed in this'instance of a length of brass tubing.Surrounding this tube substantially from end to end, is a helical fin 8,formed of a continuous strip of aluminum wound spirally on the tube.Preferably, the strip 8 is formed with a base flange or foot 9, bentangularly so as to embrace the periphery of the tube 7 and swedgedthereon during the "winding process.

As previously stated, when aluminum strip is used for the heat exchangerfin, a special aluminum solder is required if the fin is to be securedto the tube by soldering. This naturally reduces the lifeof the fintube, due to the inability of aluminum solder to stand up underoperating conditions. However, by providing this angular base flange9'on the fin and swedging it on to the tube, the fin is firmly securedfrom end to end, without the need of solder or other securing means, solong as there are no strains on the extremities of the helical fin toinitiate separation. Such initial separation of the end convolutions ofthe fin can be caused during shipment of the tin tube sections or whenthey are installed in heat exchanger units, due to vibration duringoperation.

"It is to meet this requirement that the present invention provides anauxiliary fin securing device, generally indicated by the numeral 10,for securing opposite extremities of the fin to the tube. This device ispreferably composed of a length of copper wire, one end of which isformed into a ring or loop 11, of a diameter to fit over the peripheryof the tube 7 with a sliding clearance. The opposite end of the wireprovides a fin engaging member which is bent radially outwardly from thering 11 as at 12, and in the simplest embodiment, shown in Figures 1 and3, terminates in a right angular projection 13, lying parallel with theaxis of the tube 7.

The method of applying these fastening devices comprises first, drillinga series of aligned holes 14 through a predetermined number ofsuccessive helixes of the fin strip 8 from each extremity of thefabricated fin tube 6. A fastening device 10 is then applied at each endof the tube by slipping rings 11 over the respective ends of tube 7 andinserting their angular projections 13 through the aligned holes 14 asshown in Figure 3. The rings 11 after being brought into juxtapositionto the extreme outer helixes at each end of the tube, are soldered tothe tube with regular tin-lead solder and an organic flux, byconventional means. Thus, with the rings 11 permanently fixed to thetube 7 and the projections 13 mechanically engaging the fin strip ateach end of the tube, the fin is secured against radial or peripheraldisplacement with respect to the tube, to maintain the rigid engagementof the fin with the periphery of the tube.

In the preferred embodiment of the invention shown in Figure 4, theprojection 13a is in the form of a hook which engages a hole 14 in atleast one helix at each end of the tube. The projections 13a areinserted in the respective holes 14 and then bent over against the innersurfaces of the fin strip. Otherwise, the fastening device and method ofapplication are the same as previously described.

Thus, with both forms of the invention illustrated, it will be seen thatby firmly anchoring the ring of the fastening device to the periphery ofthe tube and mechanically connecting the other end of the device to oneor more helixes of the fin strip, any movement of the end helix whichmight otherwise initiate displacement of the base of the fin, isprevented. Furthermore, by the use of tin-lead solder the anchoring ofthe fastening rings to the periphery of the tube is permanent and theauxiliary fastening device remains effective throughout the life of theequipment.

It should also be noted that the very simplicity of this invention andthe ease with which it may be applied, greatly facilitates thefabrication of finned tube sections for heat exchanger units.

- From the foregoing it is believed that the invention may be readilyunderstood by those skilled in the art without further description, itbeing borne in mind that numerous changes may be made in the details ofconstruction without departing from the spirit of the invention as setforth in the following claims.

I claim:

1. In a finned tube for heat exchangers, including a tubular core and afin strip helically wound thereon with its inner edge from end to end,continuously secured to the periphery of said core and its outer edgeprojecting radially from the core; an auxiliary fastening device for theopposite extremities of said strip, each comprising an anchoring memberrigidly connected to the periphery of the core, a connecting memberintegral with said anchoring member, offset radially from the peripheryof said core and terminating in a projection which transverselypenetrates at least one helix of said fin strip.

2. In a finned tube for heat exchangers, including a tubular core and afin strip helically wound thereon with its inner edge from end to end,continuously secured to the periphery of said core and its outer edgeprojecting radially from the core; an auxiliary fastening device for theopposite extremities of said strip, each comprising an anchoring ringembracing the periphery of said core, a connecting member integral withsaid ring, oflset radially from the periphery of said core andterminating in a projection which transversely penetrates at least onehelix of said fin strip.

3. In a fin tube for heat exchangers, including a tubular core and a finstrip helically Wound thereon with its inner edge from end to end,continuously secured to the periphery of said core and its outer edgeprojecting radially from the core; an auxiliary fastening device for theopposite extremities of said strip, each fastening device being formedof copper wire and comprising an anchoring ring adapted to be solderedto the periphery of said tube, a connecting member integral with saidring, offset radially from the periphery of said core and terminating ina projection which transversely penetrates at least one helix of saidfin strip.

4. In a fin tube for heat exchangers, including a core formed of a brasstube and a fin strip of aluminum, helically wound thereon with its inneredge from end to end, continuously swedged to the periphery of saidbrass tube and its outer edge projecting radially from said tube; anauxiliary fastening device for the opposite extremities of said strip,each fastening device being formed of copper wire and composing ananchoring ring adapted to embrace the periphery of said tube andsoldered thereto, a connecting member integral with said ring, offsetradially from the periphery of said tube and terminating in a projectionwhich transversely penetrates at least one helix of said fin strip.

5. In a fin tube for heat exchangers as claimed in claim 4, wherein saidprojection comprises a straight finger penetrating a series of helixesand lying in a plane parallel to the axis of the tube.

6. In a fin tube for heat exchangers, as claimed in claim 4-, whereinsaid projection comprises a hook shaped member which projects through atleast one helix at each end of the tube and is bent angularly to embracethe opposite face of the helix.

References Cited in the file of this patent UNITED STATES PATENTS1,972,230 Lehman Sept. 4, 1934

